An electrochromic device is capable of varying its light transmission in response to a voltage applied between two electrodes on the device, and can be used for applications such as mirrors or windows of vehicles, buildings, etc. As shown in FIGS. 1 and 2, a conventional electrochromic device includes two glass substrates 15, two transparent electrodes 14 formed respectively on the glass substrates 15, and an electrochromic laminate sandwiched between the two transparent electrodes 14. The electrochromic laminate includes an active layer 12, an ion storage layer 13, and a polymer electrolyte 11 sandwiched between the active layer 12 and the ion storage layer 13. The polymer electrolyte 11 includes an adhesive material and thus can bond the active layer 12 and the ion storage layer 13 together. The active layer 12 is made of an electrochromic material, such as tungsten trioxide (WO3) . The ion storage layer 13 is made of a material which can undergo reversible oxidation and reduction reactions, such as nickel oxide. The transparent electrodes 14 are made of, for example, indium tin oxide.
Due to generation of internal stress of the polymer electrolyte 11 resulting possibly from irradiation of ambient light or changes in temperature of the electrochromic device in use, the polymer electrolyte 11 may suffer from thermal shrinkage after a period of use. The conventional electrochromic device thus may have a plurality of undesirable shrinkage lines 17 at its periphery 16 as shown in FIGS. 1 and 2. Although the polymer electrolyte 11 may have an increased thickness to address such problem, the electrochromic device with a thick polymer electrolyte 11 would have a slow response speed in response to a voltage applied between the transparent electrodes 14.